Wells for recovering oil, gas and the like are typically created by drilling into an underground source using a hollow drill string supported in a drilling rig. The drill string includes a drill bit at the lower end that is rotated into the ground to create a wellbore. As the drill bit is rotated, drilling fluid is pumped down through the interior of the drill string to pass through the bit and return to the surface in the wellbore external to the drill string. The drilling fluid acts to lubricate the drill bit and carries the loose solids created by the drill bit to the surface. At the surface, the used drilling fluid is collected and recycled by removing some or all of the solids. The viscosity or solids content of the drilling fluid can be varied depending on the stage of the drilling process and the location of the drill bit below the surface.
Equipment and methods for handling the drilling fluid to remove solids in order to recycle the fluid are well known. Settling tanks, shale shakers, flocculating tanks and centrifuge or cyclone separators can be interconnected to handle the drilling fluids from a drill site and separate the used drilling fluid and undesirable solids for subsequent recycling of the drilling fluid. Canadian Patent No. 2,219,053 issued May 25, 1999 to Grand Tank (International) Inc. discloses an arrangement of settling tanks and centrifuges to achieve this result.
Presently, a mud storage tank to hold drilling fluid and a shale shaker to perform screening of larger solids tend to be standard equipment for a drilling rig. In normal well site operation, drilling fluid is circulated out of the a borehole and passed over a shale shaker which is a screen to separate large solid particles from the drilling fluid. The shale shaker is generally positioned directly above the mud storage tank. The rest of the equipment for solids handling including a settling tank, a shale bin for collecting solids for disposal, centrifuges and a flocculent tank tends to be available as individual pieces of equipment that must be delivered to the well site in separate loads. It is important to choose compatible equipment that is interconnectable and that is properly sized to be of appropriate capacity to work with other selected equipment. Once delivered to the site, the various pieces of equipment must be assembled together. Generally, a picker truck is needed to lift the centrifuge equipment onto a conventional raised centrifuge stand. It requires superior organization and scheduling skills to ensure the components of a solids handling system are delivered in a timely manner to the work site and assembled into an efficient and reliable solids handling system.
Thus, there is a need in the industry for a solids handling system for drilling fluid at a well site that avoids the logistical and assembly problems of the prior art.
Further, there is a need in the industry for an improved settling tank for use in separating a solids containing fluid, such as drilling fluid, which may or may not be used as a component of a solids handling system. Additionally, there is a need for an improved method of separating and/or clarifying the solids containing fluid.